1. Technical Field
The present invention relates to an image forming apparatus that obtains a density value of a non-image area of a printed sheet and predicts, based on the density value, occurrence of a noise on a printed sheet to be made later on, and an image noise prediction method.
2. Description of Related Art
Various methods for detecting a noise on a printed sheet have been suggested, and an example of such methods is disclosed by Japanese Patent Laid-Open Publication No. 2011-137895. In an image forming apparatus disclosed by Japanese Patent Laid-Open Publication No. 2011-137895, an image reader reads a test image formed on a recording medium (that is, a printed sheet), and a divider divides the read image into divisions based on the average density of each pixel array in a sub-scanning (or a main-scanning) direction of the read image such that average-density variations among the pixel arrays in each of the divisions are within a predetermined density range. A white void detector sets a threshold for detection of a white void for each of the divisions and judges whether there is a white void (i.e., noise) in each of the divisions with reference to the threshold for each of the divisions.
In an image forming apparatus, it sometimes happens that, during a continuous printing operation, a noise that is almost invisible on an earlier printed sheet becomes visible on a later printed sheet. In a conventional noise detection method, however, existence or non-existence of a noise is determined only based on a result of a test conducted on a test image formed on one sheet, and therefore, it is difficult to predict a noise at the time of occurrence of a latent noise.